This invention relates to a switching system for telecommunication and more particularly to a teletypewriter loop switching matrix for interconnecting and switching teletypewriter or data signals. Historically, teletypewriter signal loops have been characterized by a high D.C. voltage source (100 to 200 volts) in series with a resistance which could be adjusted to obtain either 20- or 60-milliampere current to operate the receiving equipment. This standard was primarily devised to operate teletypewriter units in a series connection for field applications. This arrangement permitted the operation of high resistance loops which could stretch over many miles of wire lines. These high voltage and high resistance circuits are also useful for maintaining a low bias distortion when driving high inductance selector magnets in teleprinters as well as a high signal-to-noise ratio in the presence of dirty distributor contacts or other noise sources. However, when the signal loops are confined to a fixed location, such as a structure, ship or submarine, and the selector magnets within the equipment are not driven directly, as in most existing equipment, there is no real requirement for high voltage current loops. Under such short fixed loop conditions, most of the power in the loop is dissipated in fixed or adjustable resistors within the equipment, which can cause heating problems in the equipment, Furthermore, the direct switching of one or more receiving devices to each sending device poses additional problems when a single series loop is used to interconnect the equipment. Since the loop current is a function of the impedances of the devices in series, it needs to be adjusted each time a device is switched in or out of the series loop. When devices requiring different loop currents or one of the bipolar standards are included in the system, the situation becomes impossible without the inclusion of special interface equipment required to meet the varying standard requirements. Most of the new equipment is configured for the low level bipolar standards. This causes a problem of interconnecting older devices operating on the current standards with the bipolar standards now in use. It is thus desirable to have a switching matrix which can overcome the above-mentioned problems.